We have extended our studies to show that unicellular organisms make vertebrate hormones. In extracts of Tetrahymena pyriformis, in addition to insulin-like material, we find a relaxin-like protein that behaves like relaxin in regard to solubility, charge size, and immunological activity. Additional studies in extracts of tissues of rodents, Sprague-Dawley rats, ob/ob mice and their thin littermates, control and diabetic Chinese hamsters have confirmed our previous findings of the presence of an insulin-like material. Although brain and liver membrane receptors are influenced by circulating plasma insulin, the insulin-like tissue content of the same tissues are not influenced. An extension of the presence of insulin receptors in brain and liver membranes was extended to chicken embryos. Insulin receptors are present in embryo heads and bodies by day 4 of incubation. Binding of labeled insulin increases on brain and liver membranes from 8 to 18 days of incubation in accordance to distinct developmental patterns in the two tissues.